The demand for cranes of ever-increasing size and lifting capacity has created some rather basic departures from traditional crane boom design standards, particularly for hydraulically operated telescoping booms. For example, U.S. Pat. No. 4,327,533, issued May 4, 1982, discloses an arrangement utilizing a single hydraulically operated extension and retraction cylinder for a five-section massive telescoping boom in cooperation with biased locking pins for the individual boom sections.
U.S. Pat. No. 3,921,817 discloses a latching and pin locking mechanism for the manual fly section of a multi-section telescoping boom requiring manipulations by an attendant at ground level when the boom is in a horizontal position.
The above-referenced patent application discloses a remotely operable latch and locking pin arrangement for the manual fly section of a multi-section telescoping boom, avoiding the necessity for extending hydraulic lines and/or electrical cables forwardly on the boom to the fly section or locations near the fly section.
Consistent with these developments in an overall effort to render the construction and operation of telescoping booms practical and safe in light of the above basic changes, the present invention seeks to provide an automatic safety indicator whereby the crane operator will know with certainty that the biased locking pin or pins for the boom fly section is fully engaged. Toward this end, a movable visual indicator element on the boom easily viewable from the crane operator's cab is mechanically coupled with the biased locking pin for the boom fly section so that whenever this pin becomes fully engaged or active to secure the fly section the indicator element will unfailingly move to the viewing or indicating position. In concert with this feature of the invention, a retract mechanism for the biased locking pin includes a power actuator on the boom base section which has the ability to bridge or reach across at least one intermediate telescoping boom section to cause power retraction of the biased locking pin or pins to an inactive position relative to the boom fly section.
Other features and advantages of the invention will become apparent during the course of the following detailed description.